Diamond Tiger,
A couple of years back, my daughter had a small tender area that was concerning her and it turned out to be just fine. The GP did send her for an ultrasound but it was a small breast cyst and they apparently can get bigger and more tender before period and then go down again after. I think that there are a number of different types of lumps or harder areas and they're really common and certainly not breast cancer. Personally, I'd get it checked for peace of mind though, just to be sure. take care there.